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List two differences between… (Class 10 Science 2024, Q30)

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ScienceCBSE Class 10 · Board exam 2024, set 31/4/1 · 3 marks · Short answer

CBSE Class 10 Science 2024: question 30

Set in the CBSE Class 10 board exam of 2024, paper 31/4/1, section C, question 30, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q30 · 3 marks · Short answerHeredity

List two differences between dominant traits and recessive traits. What percentage of pea plants in the generation were with yellow seeds in Mendel's cross between the pea plants having yellow (YY) and green coloured (yy) seeds ?

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 31/4/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Think about which trait shows in a hybrid Yy plant.

Hint 2

Work out the F₁ genotype, then self it and count the plants having at least one Y.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. Difference 1: when both factors are present together (as in Yy), the dominant trait is expressed, whereas the recessive trait is not expressed.

    1 mark

  2. Difference 2: a single copy of the dominant factor is enough for the trait to show, whereas the recessive trait shows only when both copies are recessive (yy).

    1 mark

  3. Cross: YY × yy gives F₁ all Yy (yellow). Selfing F₁ (Yy × Yy) gives F₂ in the ratio YY : Yy : yy = 1 : 2 : 1. Yellow (YY + Yy) = 3/4, so 75% of the plants had yellow seeds.

    1 mark

Answer: 75% of the F₂ plants had yellow seeds.

Where the marks are

  • First difference between dominant and recessive traits (1 mark)
  • Second difference (1 mark)
  • 75% yellow seeds in F₂ (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Heredity, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 31/4/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.